This invention relates to a miniaturized unidirectional electret microphone which employs an electret as a diaphragm and has a unidirectional characteristic.
In a conventional unidirectional electret microphone, a diaphragm, a back electrode and a back electrode holder are formed as a diaphragm unit, and an impedance converter for converting the microphone output into a low-impedance output is housed in a rear compartment to form an impedance converter unit; and the diaphragm unit and the converter unit are disposed in a case in its axial direction and fixed to each other. Since the diaphragm unit and the impedance converter unit thus separately prepared are combined, the conventional electret microphone has the defect that the length in its axial direction, that is the thickness, is large. The combination of such separate units calls for many parts, resulting in increased manufacturing cost. Further, the directional characteristic of the microphone is adjusted before the diaphragm unit is assembled with the impedance converter unit; but, for re-adjustment of the directional characteristic after assembling, it is necessary to disassemble the diaphragm unit from the case, and this is very troublesome.
An object of this invention is to provide a unidirectional electret microphone which can be reduced in thickness.
Another object of this invention is to provide a unidirectional electret microphone which is small in the number of parts used, easy to assemble and hence can be produced at low cost.
Another object of this invention is to provide a unidirectional electret microphone which permits easy re-adjustment of its directional characteristic.
Still another object of this invention is to provide a unidirectional electret microphone whose parts are mostly in common to a non-directional electret microphone.